Apparatus for multipolar magnetization

ABSTRACT

An apparatus comprises an annular magnetically permeable main body having a width not smaller than the width of a sheet to be magnetized and formed with a small gap. The magnetically permeable body has a conductor wound therearound and a pair of magnetic poles opposing each other with the gap interposed therebetween. Alternating current is passed through the conductor to magnetize the sheet for use in the manufacture of flexible permanent magnets which is continuously travelled on the pair of magnetic poles.

O United States Patent 1191 1111 3,858,136 Jun 1 Dec. 31, 1974 1APPARATUS FOR MULTIPOLAR 2,715,659 8/1955 Ibuka et al. 179/1002 c2,939,920 6/1960 Leilich 179/1002 C MAGNETIZATION 3,140,361 7/1964Eldridge 179/100.2C [75] Inventor: Sekiba Jun, Kyoto, Japan [73]Assignee: Yamauchi Rubber Industry Co., P i E i -G. Har is -1 Osaka,Japan Attorney, Agent, or FirmDepaoli & OBrien [22] Filed: Dec. 5, 1973[21] Appl. No.: 421,948 [57] ABSTRACT An apparatus comprises an annularmagnetically per- [30] Forelgn Apphcatlon Pnomy Data meable main bodyhaving a width not smaller than the Dec. 7, 1972 Japan 47-123148 widthof a sheet to be magnetized and formed with a small gap. Themagnetically permeable body has a [52] U.S. Cl. 335/284, 179/100.2 Cconductor wound therearound and a pair of magnetic [51] Int. Cl...H01f13/00 poles opposing each other with the gap interposed FieldSearch 3 /2 1 1002 therebetween. Alternating current is passed through100.2 R, 17 9/1002 CF the conductor to magnetize the sheet for use inthe manufacture of flexible permanent magnets which is [56] ReferencesCited continuously travelled on the pair of magnetic poles.

UNITED STATES PATENTS 6 C 10 D F 2,711,945 6/1955 Kornei 179/1001 crawmg gums PATENT ED mass 1 1974 SHEET 20F 3 F19. 6.

3 2 F Q 93 M5 Frequency (H 3 2 533 33* at: UM

m b: q

Speed of travel (m/min) Current PAIENTED I 3,858,136

SHEET 30F 3 Fig.4.,

1v 9 5 4 IS mar/r zvmw M T II SUI Attracting force SI 2cm") Size of gap(mm) A 5.5 MN 55 /v A/ .535" /v NSJMA'SS/W/JSM/JSN WI I I I I I I IAPPARATUS FOR MULTIPOLAR MAGNETIZATION BACKGROUND OF THE INVENTION Thepresent invention relates to apparatuses for multipolar maggnetizationfor use in the manufacture of flexible permanent magnets, moreparticularly to a multipolar magnetizing apparatus for use in themanufacture of flexible permanent magnets in the form of an elongatedsheet.

In recent years, flexible permanent magnets have been introduced intowide use as new industrial materials. Such flexible permanent magnet ismade by preparing an elongated sheet made of a mixture of syntheticrubber suchas styrene rubber, nitrile rubber, butyl rubber, neoprenerubber, isoprene rubber, ethylenepropylene rubber and chlorosulfonatedpolyethylene or synthetic resin such as vinyl chloride, polyethylene,chlorinated polyethylene and ethylene-vinyl acetate copolymer and apowdered magnetic material such as barium ferrite of l to 7 microns inthe weight ratio of 1:5 to 10 and magnetizing the powdered magneticmaterial in the sheet. Since the flexible permanent magnet is in theform of a sheet, a great number of N poles and S poles must be arrangedalternately. Multipolar magnetizing apparatuses have been developed tofulfil such requirement.

Apparatuses for multipolar magnetization heretofore known comprise amagnetically permeable body in the form of a flat plate having a greatnumber of parallel grooves and a conductor fitted in the grooves in azig-' zag manner. With such apparatus a high voltage direct current isintermittently passed through the conductor to magnetize a sheet to bemagnetized which is travelled intermittently in timed relation to theapplication of the current. Accordingly, the conventional apparatusrequires a power source of the charging and discharging type and ismoreover inefficient inasmuch as it is not adapted for continuousmagnetization. For efficient operation, therefore, there is a need touse a large magnetizing area and a high voltage source of severalthousand volts, this rendering the apparatus costly and hazardous.Furthermore since it is necessary to vary the distance between themagnetic poles to be formed in accordance with the thickness of thesheet to be magnetized, a suitable number of multipolar magnetizingapparatuses must always be prepared which have varying interpoledistances, but this needs the replacement of apparatus, entailing acorresponding reduction in work efficiency. In addition, it isimpossible to form grooves of a small width of less than I mm in theflat plate-like magnetically permeable body because of the difficultiesencountered in machining and insulation. Further conventionally, a sheetmaterial is subjected to multipolar magnetization on its oppositesurfaces by employing a pair of the above-mentioned multipolarmagnetizing apparatuses in facing relation, with their magnetic polespositioned in register with each other and applying current to both theapparatuses at the same time. According to this method, however, it isdifflcult to assure fully satisfactory magnetization on the oppositesurfaces of the sheet due to errors and the like involved in groovingthe magnetically permeable body.

SUMMARY OF THE INVENTION The present invention provides an apparatus formultipolar magnetization for use in the manufacture of flexiblepermanent magnets which has overcome the problems described above andwhich comprises an annular magnetically permeable body having a widthnot smaller than the width of a sheet to be magnetized and formed with agap, a conductor wound around the magnetically permeable body andconnected to an alternating current source to thereby pass constantexciting current of constant frequency therethrough and a pair ofmagnetic poles opposing each other with the gap which measures from I to2.5 mm in size interposed therebetween and each having a surface to bepositioned face-to-face with the sheet to be travelled continuously formagnetization. With the apparatus of this invention, the space betweenthe magnetic poles to be formed in the sheet by magnetization can bereadily varied by one of the following two methods. Firstly, thefrequency is changed. Alternatively, the speed of travel of the sheet tobe magnetized is changed. By altering the space between the magneticpoles formed by magnetization in the sheet of a given thickness theattracting force imparted to the magnetized sheet changes in accordancewith the space between the magnetic poles. Thus to impart a maximumattracting force to the sheet of flexible permanent magnet, there is aneed to set an optimum interpole space in corresponding relation to thethickness of the magnet. Generally, it is preferable that if the sheetof magnet has a large thickness, the interpole space be large, and asmall interpole space for the sheet of a small thickness. According tothe apparatus of this invention, the space between the magnetic polesformed by magnetization can be varied continuously by the foregoingmethods, so that it is easy to find by experiment an optimum interpolespace in corresponding relation to the thickness of a sheet to bemagnetized. This makes it sure that sheets of flexible permanent magnetof varying thicknesses can be given the greatest attracting forcesrespectively by one multipolar magnetizing apparatus. The presentapparatus further assures an efficient operation inasmuch as the sheetto be magnetized is travelled continuously for magnetization. Theapparatus imparts uniform magnetism to the magnetized sheet to improvethe quality of the product because it is easy to maintain the input at auniform level. Since magnetization can be achieved with applications ofa small current of low voltage, electric equipments for the apparatusare inexpensive and less hazardous. Furthermore, when a pair of the sameapparatuses according to this invention are to be used with simultaneousapplication of current to magnetize a sheet on its opposite surfaces,the magnetizing poles can be positioned in register with each othereasily, since the apparatus has only one pair of the poles, henceaccurate magnetization.

This invention will be described below in greater detail with referenceto the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a plan view showing aconventional multipolar magnetizing apparatus and a sheet while thesheet is being magnetized thereon;

FIG. 2 is a view in transverse section taken along the line II-II inFIG. 1;

FIG. 3 is a perspective view showing an embodiment of multipolarmagnetizing apparatus according to this invention;

FIG. 4 is a perspective view showing another embodiment of thisinvention;

FIG. 5 is a fragmentary perspective view showing a modification of theembodiment of FIG. 3 in which the gap between a pair of magnetic polesis filled with synthetic resin;

FIG. 6 is a graph showing the relation between the frequency ofalternating current used for magnetization and the attracting force ofmagnetized sheet;

FIG. 7 is a graph showing the relation between the speed of travel of asheet to be magnetized during magnetizing operation and the attractingforce of magnetized sheet;

Hg. 8 is a graph showing the relation between the size of the gapbetween a pair of magnetic poles and the attracting force of magnetizedsheet;

FIG. 9 is a diagram showing the relation between the frequency ofalternating current used for magnetization and the space betweenmagnetic poles formed by magnetization and;

FIG. 10 is a diagram showing the relation between the speed of travel ofa sheet to be magnetized and the space between magnetic poles formed bymagnetization.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIGS. 1 and2, a conventional apparatus for multipolar magnetization comprises aplatelike magnetically permeable body 2 formed with parallel grooves Iin its upper surface, a conductor 3 fitted in the grooves l continuouslyin a zigzag manner and a greater number of magnetic poles 4 and 5alternately arranged and formed between the grooves 1. An elongatedsheet 6 for use in the manufacture of flexible permanent magnets to bemagnetized is made of a flexible material incorporating therein bariumferrite powder or like powder to be magnetized. For magnetization,oneend portion of the sheet 6 is placed on the magnetizing apparatus anddirect current is passed through the conductor 3, whereby magnetic polesare formed in the portions of the sheet 6 which portions are in contactwith the'magnetic poles 4 and 5. Thus a number of N poles and S polesare formed at the same time although partially withrespect to thelongitudinal direction of the sheet 6. The magnetized area A1 of thesheet 6 corresponds to the surface area of the magnetizing apparatus.After the magnetization of area Al, the sheet 6 is moved by an amountcorresponding to the area Al in the direction of the arrow in FIG. 1.During this movement, supply of current to the conductor 3 isinterrupted. Subsequently when an area A2 of the sheet 6 is positionedon the magnetizing apparatus, current is applied to the apparatus formagnetization. In this way, the sheet 6 is thereafter transportedintermittently to form the magnetic poles throughout the entire area ofthe sheet 6 in parallel arrangement in the longitudinal direction,whereby a sheet of flexible permanent magnet is obtained. It will bereadily understood that such conventional multipolar magnetizingapparatus has the drawbacks already described.

FIG. 3 shows an embodiment of multipolar magnetizing apparatus accordingto this invention. The apparatus includes a circular cylindricalmagnetically permeable body 13 having a small gap 12 in its top. Themagnetically permeable body is made of parmalloy, but iron-nickel alloy,silicon steel, pure iron, carbon steel, nickel, cobalt and like materialare also usable. A sheet 11 for use in the manufacture of flexiblepermanent magnets to be magnetized is substantially the same as thesheet 6 described above. The cylindrical, magnetically permeable body 13has a width almost equal to that of the sheet 11. Of course, the body 13must have a width not smaller than the width of the sheet 11 to bemagnetized. The cylinddrical, magnetically permeable body 13 is providedwith a conductor 14 wound therearound and has a pair of magnetic polesl5 and 16 opposing each other with the gap 12 interposed therebetween.The magnetic poles 15 and 16 have smooth upper surfaces 15a and 16a tobe positioned face-toface with the sheet 11 to be magnetized. Theconductor 14 is connected to an alternating current source and therebyconstant exciting current of constant frequency is continuously passedtherethrough to magnetize the sheet 11 which is adapted to be travelledcontinuously in the direction of the arrow in FIG. 3 in facing relationto the pair of magnetic poles 15 and 16. To increase the effective fluxabove the gap 12, the magnetic poles 15 and 16 are tapered toward theportions where they oppose each other. However, the opposing portionsmust not be sharp edges so as not to arrest the sheet 11. Preferably,the conductor 14 may be positioned closer to the magnetic poles 15 and16 than is illustrated in the drawing, since the closer the conductor 14is positioned to the magnetic poles l5 and 16, the lower will be thepower required and the greater will be the magnetic flux to be produced.

FIG. 4 shows another embodiment of multipolar magnetizing apparatusaccording to this invention. The apparatus includes an annularmagnetically permeable body 23 having a substantially rectangularsection and formed with a small gap 22 in its top. A continuousconductor 24 is wound around the opposing walls of the magneticallypermeable body 23. Magnetic poles 25 and 26 have smooth upper surfaces25a and 26a to be positioned face-to-face with a sheet to be magnetizedand oppose each other with the gap 22 interposed therebetween.

FIG. 5 shows a modification of the multipolar magnetizing apparatusshown in FIG. 3 wherein the gap 12 is packed with synthetic resin 17.During magnetization, fragments of the sheet to be magnetized, iron andthe like are liable to accumulate in the space of the gap 12 to reducethe effective magnetic flux. The synthetic rein 17 packed in the gap 12serves to obviate such objection. The same parts as in FIG. 3 arereferred to by the same reference numerals and characters as in FIG.

FIG. 6 illustrates the relation between the frequency of alternatingcurrent applied to the multipolar magnetizing apparatus of FIG. 3 tocarry out magnetizing operation and the attracting force of themagnetized sheet obtained. The attracting force is plotted as ordinateand frequency as abscissa. The size 1 of the gap 12 is 1 mm, thethickness of the sheet 11 to be magnetized is 0.6 mm, the speed of thesheet 11 travelled above the magnetic poles 15 and 16 is 8 m/min, thevoltage of alternating current input is 200 V and the amperage of thesame is 3 A. Under these conditions, the frequency of the input isvaried with the result that an attracting force of about 40 g/2 cm isobtained at about 50 Hz as seen in FIG. 6.

FIG. 7 shows the relation between the speed of travel of the sheet to bemagnetized and the attracting force of the sheet magnetized by the sameapparatus as above. The attracting force is plotted as ordinate and thespeed of travel as abscissa. The conditions are the same as in the caseof FIG. 6 except that the frequency of the input is 50 Hz and the speedof travel is varied. FIG. 7 indicates that a speed of travel of about 8m/min gives a maximum attracting force of about 40 g/2 cm FIG. 8 showsthe relation between the size of gap of the same apparatus as above andthe attracting force of the magnetized sheet. The attracting force isplotted as ordinate vs. the gap size as abscissa. The conditions are thesame as in the case of FIG. 6 except that the frequency of input is 50Hz, with the gap size made variable. FIG. 8 reveals that the gap sizeranging from I to 2.5 mm gives the greatest attracting force which isabout 40 g/2 cm FIGS. 6 to 8 indicate that the apparatus of thisinvention imparts an attracting force of about 40 g/2 cm to a sheet of0.6 mm in thickness when it is magnetized. If a sheet has an attractingforce of 30 g/2 cm the sheet is serviceable as a flexible permanentmagnet for some uses. Although it has heretofore been necessary toincrease the thickness of the flexible magnet sheet if it is desired toobtain a great attracting force, the present invention makes it possiblefor a thin sheet to have a high attracting force and therefore providesflexible magnets which are applicable to a wider variety of uses.

FIG. 9 shows the relation between the frequency of alternating currentused for magnetization and the space between the magnetic poles formedby magnetization. Current is plotted as ordinate vs. time as abscissa.The sheet 11 to be magnetized is arranged in parallel to the abscissa toshow the interpole space in corresponding relation to the frequency. InFIG. 9, section Bl indicates magnetic poles obtained at a mediumfrequency, section B2 those obtained at a low frequency and section B3those obtained at a high frequency. If the frequency is low, the spacebetween the magnetic poles is large, whereas a high frequency gives anarrow interpole space.

FIG. 10 shows the variations in the space between the magnetic polesformed by magnetization using alternating current having a constantfrequency and changing the speed-of travel of the sheet 11 to bemagnetized. In FIG. 11, section C1 indicates the result achieved at amedium speed of travel, section C2 that achieved at a high speed oftravel, section C2 that achieved at a high speed of travel and sectionC3 that achieved at a low speed of travel. A fast speed of travelproduces an increased interpole space, whereas a slow speed gives anarrow interpole space.

If the interpole space is P (mm) and frequency is f in the case wherealternating current is used, the speed of travel V is given by:

V= P XfX 120 1,000 m/min.

The present invention may be practiced in other different modes withoutdeparting from the spirit and basic features thereof. Accordingly, theembodiments herein disclosed are to be construed as being illustrativeonly but not as limitative in every respect. The scope of this inventionis defined by the appended claims rather than by the foregoing detaileddescription, and all the modifications and alternations within a scopeequivalent to that of the claims are to be covered by the claims.

What is claimed is:

1. An apparatus for multipolar magnetization for use in the manufactureof flexible permanent magnets, comprising an annular, magneticallypermeable body formed with a gap and having a width not smaller than thewidth of a sheet to be magnetized, a conductor wound around said bodyand connected to an alternating current source to thereby pass constantexciting current of constant frequency therethrough and a pair ofmagnetic poles opposing each other with said gap which measures from 1to 2.5 mm in size interposed therebetween and each of said poles havinga surface to be positioned face-to-face with said sheet as the sheettravels continuously thereover for magnetization.

2. The apparatus as set forth in claim 1 wherein said frequency is 50hz.

3. The apparatus as set forth in claim 1 wherein said gap is packed withsynthetic resin.

4. An apparatus for multipolar magnetization for use in the continuousmanufacture of flexible permanent magnets from a continuously movingsheet, comprismg:

A. an annular, magnetically permeable body, having:

1. a longitudinally disposed axis,

2. a width, measured in parallel to said axis, which is not smaller thanthe width of said sheet,

3. a pair of magnetic poles in parallel and opposed relationship anddisposed in parallel to said axis, said poles having a gap therebetweenmeasuring from 1 to 2.5 mm and each of said poles having a flat surfacedisposed in parallel to said axis, said flat surfaces being in a commonplane, and

B. a conductor which is wound around said body and is connected to asource of uninterrupted alternating current of constant frequency,amperage, and voltage.

5. The apparatus of claim 4 wherein said apparatus is capable ofgenerating an attracting force of 40 g/2cm in said sheet when said gapis 1 mm in size, said frequency is 50 Hz, said voltage is 200 volts,said amperage is 3 amperes, and said sheet is formed of a flexiblematerial incorporating barium ferrite powder therein, has a thickness of0.6 mm, and travels at 8 meters per minute over said flat surfaces.

6. The method of continuously generating at least 40 g/2cm in a sheet offlexible material containing a powdered magnetic material and having athickness of about 0.6 millimeters comprising passing said sheetcontinuously at a speed of about 8 meters per minute over a pair ofclosely adjacent magnetic poles which lie in a common plane and areseparated by a gap of l-2.5 millimeters and generate a magnetic fluxcreated by a constant alternating current frequency of 50 Hz. a constantvoltage of 200 volts, and an amperage of 3 amps. =l

1. An apparatus for multipolar magnetization for use in the manufactureof flexible permanent magnets, comprising an annular, magneticallypermeable body formed with a gap and having a width not smaller than thewidth of a sheet to be magnetized, a conductor wound around said bodyand connected to an alternating current source to thereby pass constantexciting current of constant frequency therethrough and a pair ofmagnetic poles opposing each other with said gap which measures from 1to 2.5 mm in size interposed therebetween and each of said poles havinga surface to be positioned face-to-face with said sheet as the sheettravels continuously thereover for magnetization.
 2. The apparatus asset forth in claim 1 wherein said frequency is 50 hz.
 2. a width,measured in parallel to said axis, which is not smaller than the widthof said sheet,
 3. The apparatus as set forth in claim 1 wherein said gapis packed with synthetic resin.
 3. a pair of magnetic poles in paralleland opposed relationship and disposed in parallel to said axis, saidpoles having a gap therebetween measuring from 1 to 2.5 mm and each ofsaid poles having a flat surface disposed in parallel to said axis, saidflat surfaces being in a common plane, and B. a conductor which is woundaround said body and is connected to a source of uninterruptedalternating current of constant frequency, amperage, and voltage.
 4. Anapparatus for multipolar magnetization for use in the continuousmanufacture of flexible permanent magnets from a continuously movingsheet, comprising: A. an annular, magnetically permeable body, having:5. The apparatus of claim 4 wherein said apparatus is capable ofgenerating an attracting force of 40 g/2cm2 in said sheet when said gapis 1 mm in size, said frequency is 50 Hz, said voltage is 200 voLts,said amperage is 3 amperes, and said sheet is formed of a flexiblematerial incorporating barium ferrite powder therein, has a thickness of0.6 mm, and travels at 8 meters per minute over said flat surfaces. 6.The method of continuously generating at least 40 g/2cm2 in a sheet offlexible material containing a powdered magnetic material and having athickness of about 0.6 millimeters comprising passing said sheetcontinuously at a speed of about 8 meters per minute over a pair ofclosely adjacent magnetic poles which lie in a common plane and areseparated by a gap of 1-2.5 millimeters and generate a magnetic fluxcreated by a constant alternating current frequency of 50 Hz, a constantvoltage of 200 volts, and an amperage of 3 amps.